The present invention relates to an improved solar fluid heating apparatus. More particularly, the present invention relates to an easily transportable solar fluid heating apparatus wherein circulation of the flowable heat carrier medium to and from a reservoir is achieved, without the requirement of an additional pump, by changes in the density of the heated fluid medium.
French Patent No. 1,097,233, published July 1, 1955, and Swiss Patent No. 246,216, published Sept. 1, 1947, disclose that it is known generally, in rigid structures made of sheet metal, to utilize the differences in density of a medium produced by heating to provide movement of the medium in order to produce useful heat from solar radiation. According to the French patent, two profiled sheet metal plates are combined in such a manner that they form parallel flow channels in the control region of the device, and a transverse channel is disposed below and above these channels with the transverse channels being in communication with an inlet or outlet, respectively. The interconnection of this rigid conduit structure with a reservoir for the medium in such a manner that a circulation of the medium is effected through the conduit structure as well as through the reservoir is not disclosed in this patent.
The above mentioned Swiss patent discloses a rigid reservoir disposed above the conduit structure formed of sheet metal plates which are arranged at slight mutual distances. The conduit structure is in communication with the reservoir through a gap. In this device, the entire quantity of fluid in the reservoir is to be heated by means of convection. Even if the described small space between the sheet metal plates is complemented to form parallel channels, no controlled circulation of the medium results in this known structure because the medium which is heated in the conduit structure rises in all channels, i.e., over the entire cross section of the conduit structure and the still cold medium from the reservoir drops in all channels as well.
In addition to the above mentioned disadvantages and deficiencies of the above-described prior art, these rigid prior art devices suffer from the further disadvantages that they are not easily transportable and generally require some special form of fastening device such as a foundation or the like.
A type of solar fluid heating device which has an advantageous structure in that it is easily transportable and does not require any special or permanent type of fastening structure is disclosed in U.S. Pat. No. 3,022,781, issued Feb. 27, 1962 to S. Andrassy and in applicants' copending U.S. patent application Ser. No. 675,594, filed Apr. 9, 1976. The conduit structures disclosed therein are generally in the form of a coilable mat formed by selective connections between two flexible foils, e.g., of plastic, with at least one of the foils being colored so as to absorb solar radiation. In these conduit structures, it is intended to provide flow channels which are as long as possible. For this reason the connections between the various foils, which are formed, for example, by welding, are preferably arranged so that meander or serpentine shaped flow channels extend between the inlet and outlet for the heat carrier medium, which generally is water.
Finally, to round out the state of the art, reference is made to German Gebrauchsmuster (Utility Model) No. 75 24 272 which describes a water tank made of a rubber-like material that can serve, for example, as a shower. This bag-like tank is supposed to be hung in the sun so that its contents are heated by the sun's rays. In this reference, there is no teaching of the important subdivision into a flat conduit structure to heat the medium or of a reservoir for the medium.